摘要:

Abstract.Data from 15 rice‐fish experiments, conducted at the Freshwater Aquaculture Center of Central Luzon State University. Philippines during the years 1976‐1983. were analysed using the multiple linear regression technique with the objective of explaining the variation in fish production from input and climate data. The experiments dealt with the effects of various management practices on the production of Nile tilapia,Oreochromis niloticus(L.), in concurrent culture with several varieties of lowland irrigated rice,Oryzasativa(L.). Climate data were obtained from the nearest weather station.Significant models (P<0.001) were derived for gross fish yield (kg/ha), net fish yield (kg/ha), fish recovery (%), fish growth rate (g/day) and rice yield (kg/ha). For gross fish yield, 66% of the variation could be explained by seven independent variables: length of the culture period, fish stocking weight and density, nitrogen and phosphorous application rates; insecticide application and air temperature.The interpretation of the regression results is discussed. Despite the problems with linking regression coefficients to ‘real life’ processes, this kind of exploratory data analysis, applying modem statistical techniques, can be a useful tool in summarizing the results of previous research and obtaining more information from existi

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1990.tb00377.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Abstract.The effects of density, cover, and individual versus communal holding on brood size and female survival during the breeding period were examined in a large‐scale experiment, involving 3591 mature noble crayfish,Astacus astacusL., females.Crayfish density during both mating/spawning and winter incubation had major effects on egg survival. In the high density experiment (67 and 44 individuals per m2during mating/spawning and winter incubation respectively) mean pleopod egg number in April was 18‐20. Lowering the density to 50 during mating/spawning (still 44 individuals per m2during winter incubation) gave mean pleopod egg numbers of 31‐38. In the low density experiment (50 and 33 individuals per m2during mating/spawning and winter incubation) mean pleopod egg numbers were 44‐46. Egg‐bearing females held in individual compartments with perforated bottom had a mean pleopod egg number of 25.Female survival during winter incubation was high, ranging from 91.8 to 98.3%. Covering the basins had no distinct effect on egg and female survival.InAstacus astacusculture we recommend that crayfish density should not exceed about 50 individuals per m2during mating/spawning and about 33 individuals per m2during winter i

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1990.tb00378.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Abstract.This paper reports a series of trials on the cryopreservation ofOreochromis niloticus(L.) spermatozoa, using methanol as the cryoprotectant.Immotile milt samples pooled from four males were diluted with two diluents, each being subjected to equilibration periods of 15, 30, 45, 60 and 90 min. In addition, samples of fresh pooled milt were kept for 0, 2, 4, 6 and 8 days at 4°C prior to cryopreservation. Diluted samples were stored in 250‐μl plastic straws and cooled to ‐50°C at 5°C/min and held under liquid nitrogen for between 1 and 3 weeks. Viability of post‐thawed spermatozoa was estimated from video recordings of samples activated under a microscope and from fertilization rates of eggs.The type of diluent and its interaction with equilibration time significantly (P<0.05) influenced the post‐thaw motility of spermatozoa. Spermatozoa stored for up to 6 days prior to cryopreservation were as fertile as freshly frozen spermatozoa and yielded 60.6 (±SE, 8.4) develo

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1990.tb00379.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Abstract.Production of Pacific oysters was studied under pilot‐scale conditions in Baynes Sound, British Columbia, using common bottom culture strategies. Four seeding treatments, each with a different seed per cultch density were cultured: wild‐caught seed 5mm in shell height at 10 seed per cultch piece and hatchery produced seed 1‐2 mm in shell height at densities of 11, 40 and 105 per cultch piece. The cultch material for all treatments was Pacific oyster shell. All seed was reared for approximately 1 year in a seed nursery located at the 2.2‐m tidal level then transferred to a 1‐m tidal level grow‐out plot until harvest 4 years later in May 1988, Clusters of large numbers of oysters were separated and evenly distributed within the plots when the oysters attained a shell height of 60‐100 mm. During the first year, growth was slow and mortalities were relatively high. All treatments produced oysters of similar size at harvest. The proportion surviving at harvest was substantially higher for the wild oysters which were initially larger at time of planting. Within the hatchery treatments proportional survival per cultch piece was inversely related to initial density on the shell; however, total production per cultch piece was positively related to initial density. Most efficient use of seed is attained at lower densities per shell; however, most efficient use of cultch and effort to handle cultch is attained at h

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1990.tb00380.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Abstract.Two studies were conducted to determine the effects of rearing Snake River cutthroat trout,Oncorhynchus clarkiRichardson, and Eagle Lake rainbow trout,Oncorhynchus mykissRichardson, in oxygen supersaturated water. The performance of cutthroat trout held at oxygen saturation as high as 172% was compared with that of control fish held in water at or below saturation. At an oxygen saturation level of 172%, total gas pressure reached 117% in late afternoon, and nitrogen saturation was reduced to 93%. The rainbow trout were held at a maximum of 150% oxygen saturation; total gas pressure did not exceed 112% in late afternoon and nitrogen saturation was reduced to 99%. Fish growth, fin quality and feed conversions were not significantly affected in either species. At the termination of the study gas bubble disease was observed in 94% of the cutthroat trout held in oxygen supersaturated water. Gas bubble disease was not observed in rainbow trout.

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1990.tb00381.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Abstract.A total of 1680 brown trout,Salmo truttaL., from 63 different localities in Scotland were sampled and examined for 34 loci. Thirteen loci were polymorphic in one or more populations. The mean observed heterozygosity for wild populations ranged from 0.0 to 8‐9% (x=4.5%) in the same range as previous studies on this species. Within drainage studies and gene diversity analysis confirms that a large proportion (33%) of total gene diversity was distributed between populations. The Ldh‐5(100) allele was common in Scottish populations and its distribution would fit the hypothesis that this allele was indicative of an ancestral trout population in Scotland before the invasion of trout characterized by the Ldh‐5(90) allele. The results have important implications for the management of the brown trout genetic res

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1990.tb00382.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Abstract.A comparative study of ‘mpasa’,Opsardium microlepis(Günther), and ‘ntchila’,Labeo mesopsGünther, was made with regard to spawning strategy. While fractional spawning was routinely observed in mpasa, total spawning of ntchila suggests a less efficient survival strategy. Ova and oocyte counts varied from 34510 to 65657 in mpasa of 54‐57.7cm total length and were numerically higher than those observed in ntchila, which ranged from 10479 to 47957 in 19‐29.3cm fish. Gonadosomatic indices were 3.75 to 10.97 for the former and 9.66 to 16.09 for the latter fish. Because of the breeding behaviour, broodstock and hatchery management is easier with ntchila than with mpasa. This could be a basis for a culture‐based fishery which has so far been unexplored in Malawian waters. Possibilities for enhancement of the two fisheries are alluded to in light of

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1990.tb00383.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Abstract.A sampling survey of Philippine small pelagic fisheries was undertaken between 1987 and 1988 at eight sites in the Philippines. A description is given of the different fishing methods and estimates are made of catch per unit of effort and catch composition. Catches of sardines and anchovies dominated the landings of small‐scale small pelagic gears whilst roundscads were an important catch component of large‐scale fishing vessels. A first attempt to describe the overall species composition of the Philippine small pelagic landings was made using the sampling data and annual fisheries statistics for the years 1982‐1986. Ten species of scad, mackerel and anchovy comprised 75% of the Philippine small pelagic landings. These results are discussed with respect to improving monitoring and sampling programmes designed to provide management‐related info

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1990.tb00384.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Abstract.The following results were obtained from brown trout,Salmo truttaL., from the Scorff Basin between 1973 and 1984.Individual growth varied depending on the environment (brook or river, upstream or downstream) and the year. The differences were seen in young fish and the effect of different years was temperature related.In spawners there was always a greater ratio of males (the majority aged 1+ years). The majority of females matured for the first time at 2+, although 1+ females were frequent in brooks. Maturation at 1+ depended on growth at 0+.Spawning took place in tributaries downstream of the basin, in the principal river and in upstream tributaries.Survival rates were estimated in one stream, where it was confirmed that the majority of recorded mortalities were 0+ fish. In spawners, annual survival of females was better (50%) than in males (30%).A biological cycle is proposed, taking into account the existence of an intermediate generation in the brooks, which places itself between migrating spawners from the main river and juveniles (1+ and 2+) produced from the streams and ensures essential trout recruitment in the Scorff.

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1990.tb00385.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Abstract.The diet of brown trout,Salmo truttaL., in the Owendoher Stream, a tributary of the River Dodder, was examined at monthly intervals from June 1981 to May 1982. The diets of the three main age groups, 0+, 1 + and 2+/3+ fish, have been separately described and compared. Ephemeropteran nymphs, larval and adult chironomids as well as a variety of other adult insects were the most frequently consumed foods. While 0+ trout largely concentrated on aquatic organisms, adult insects, in particular those of terrestrial origin, became progressively more important in the diet with increasing age of the fish. Daily ration calculations indicated that food intake was highest during the summer and early autumn months when it was well in excess of maintenance requirements. This corresponded to a period of good growth. For the remainder of the year food intake was not much higher than maintenance requirements. In fact, 1+ and older (2+/3+) fish probably experienced an energy deficit on occasions during the winter which was reflected in their poor condition and weight loss. The relationship between growth and production in the system are further discussed.

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1990.tb00386.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY